it was a self-deluding saccharine.

If this is, who I think it is then you're full of it still - take your woe-is-me attitude, shove it and actually put your reflections, musing, thoughts or whatever trendy label you want to slap on it into practice.
If you don't start realizing you are the issue, and a common denominator as to why these "beautiful relationships" don't last, you wont find redemption. Maybe start by giving the other friend / previous relationship closure about your bad behavior.

Why'd the relationship end if she was all of those great things?

Harsh dude, harsh. And the "common denominator" quip is overused by many an amateur psychologist. To the OP, you sound like you are, based only on your confession, on the side of the good, making an attempt to wade through the muck of relationships. Good luck.

I keep coming back to read your confession because there are certain parts of it that resonate with me in regards to a past experience.

Count yourself fortunate - extremely fortunate - that you have, within a very short amount of time, been involved in two beautiful relationships. This is not the norm.

Your words convey a skill in remaining detached (in the Buddhist sense, not psycho-centric) while fully appreciating your experiences. Be careful you are indeed detached because of an awakened awareness rather than because of an psychosomatic defence response. One clue as to which technique you're employing can be seen in the relationships around/behind you: do your encounters with others leave them/you at ease? encouraged? uplifted? aggrieved? frustrated? confused?

Being honest and ending a relationship in a timely manner is mature, however did your proclamation come from a place within you that is awakened or defensive? And of course, no matter how well and amiable a break-up is there will be tears and mourning. The loss of beauty is profound and felt differently by everyone. Allow the emotional processing to unfold without judgement.

I realize this is a long comment to your post, but as I stated above, this post resonates with me. I once saw beauty and magic all around us. As it is, I've had but one beautiful intimate relationship and it did not last. My ability to recognize beauty is now greatly diminished and the magic is for the most part all used up.

Are you the type of person who sees beauty in abundance? I reckon you are and therefore, I hope you come to realize that all your beautiful words are just that: words. They can seduce and they can injure. Words certainly have power, however it's your action that quicken your words. Your actions will be the true measure. Wake up and live well.

Sounds like you really loved the ex before this last one or you wouldn't be mentioning her, saying that makes me think that you don't really know what you want in terms of that "bull shit" emotion called love in the first place. Although your confession is well written, you almost make it sound like you are too good for a relationship at all. Maybe instead of making excuses for yourself for hurting someone in your past, perhaps you should apologize to her personally and free your conscience of the negative energy your past actions are causing you. If the feelings and connection you had between each other were mutual, there's a good chance she feels the same way and would accommodate your apology and a friendship could still be a possibility. It doesn't hurt to try.

I have two comments, one has the most pluses, the other has the most minuses.

that your actions in the past were probably because you were provoked.

"There is this splinter in my mind, like a tiny sliver I can not get out."